In the prior art, apparatuses to incinerate waste such as municipal garbage have frequently employed fluidized beds. Such apparatuses blow air or the exhaust gas from incineration into the fluidized bed medium, which may be sand, from below a dispersion plate (e.g., a perforated plate) in the furnace onto which the sand is supplied. The material is heated and thereby fluidized. Waste such as municipal garbage is fed into the fluidized bed formed in this way and combusted.
The gases generated by this incineration are exhausted through a discharge line and enter a boiler. In the boiler, steam is produced through thermal contact with heated water.
The steam is used as the drive source for a turbine in an electrical plant.
Organic compounds such as vinyl chloride plastics are a component of waste material such as municipal garbage. The combustible portion contains approximately 0.2-0.5% Cl. When combusted, chlorides contained in the vinyl chloride plastics mixed in with waste material such as municipal garbage are converted to HCl. (Normally, the HCl content of the exhaust gas from the incineration of garbage is in the range of 500-1,000 ppm.) This HCl acts on the tubes in the boiler used to produce steam which is placed at the exit of the incinerator and corrodes them. At temperatures above 350.degree. C., as the surface temperature of the tubes increases, the corrosion becomes extremely serious.
It was thus necessary in prior art incinerators to keep the temperature of the tube surfaces below 350.degree. C. This limited the temperature of the steam which could be produced to approximately 300.degree. C. As a result, the generating efficiency of prior art garbage incinerators was below 15%. In contrast, fuels such as heavy oil or LNG (liquified natural gas) are virtually free of chlorine compounds. Boiler tubes in plants which burn these fuels can withstand temperatures of 500-600.degree. C., yielding an efficiency of 40%. Because of their poor efficiency, there has been a strong demand for the improvement of waste incinerators.